In this work, a third generation AI-Li alloy has been successfully spot welded with probeless friction stir spot welding （P-FSSW）, which is a variant of conventional friction stir welding. The Box-Behnken exper-imen...In this work, a third generation AI-Li alloy has been successfully spot welded with probeless friction stir spot welding （P-FSSW）, which is a variant of conventional friction stir welding. The Box-Behnken exper-imental design in response surface methodology （RSM） was applied to optimize the P-FSSW parameters to attain maximum tensile/shear strength of the spot joints. Results show that an optimal failure load of 7.83 kN was obtained under a dwell time of 7.2 s, rotation speed of 950 rpm and plunge rate of 30 mm/rain. Sufficient dwell time is essential for heat conduction, material flow and expansion of the stir zone to form a sound joint. Two fracture modes were observed, which were significantly affected by hook defect. In addition to mechanical testing, electron backscattering diffraction （EBSD） and differential scanning calorimetry （DSC） were used for microstructure evolution and property analysis. The precipitation of GP zone and AI3Li as well as the ultrafine grains were responsible for the high microhardness in the stir zone.展开更多
The development of microstructure during the aging of Ti-10V-2Fe-3A1 alloy in the 13 and （α＋β） solution-treated and quenched conditions was investigated. The results showed that the isothermal holding below 400℃...The development of microstructure during the aging of Ti-10V-2Fe-3A1 alloy in the 13 and （α＋β） solution-treated and quenched conditions was investigated. The results showed that the isothermal holding below 400℃ yielded homogeneously distributed, spherical ω-phase particles. Fine α aggregates are formed uniformly within 13 grains by nucleating at at particles or β/ω interfaces. At higher temperatures, thin martensite plates decomposed in water-quenched condition. The formation of ω phase was avoided and coarse coarse α-phase plates directly precipitated from the 13 matrix. The highest hardness values were found when the alloys were aged at 400℃ for 8 h. The significance of the observations was discussed in terms of the effect of aging on the precipitations and property.展开更多
S31042 heat-resistant steel was joined by linear friction welding （LFW） in this study. The microstructure and the mechanical properties of the LFWed joint were investigated by optical microscopy, scanning electronic...S31042 heat-resistant steel was joined by linear friction welding （LFW） in this study. The microstructure and the mechanical properties of the LFWed joint were investigated by optical microscopy, scanning electronic microscopy, transmission electron microscopy, hardness test and tensile test. A defect-free joint was achieved by using LFW under reasonable welding parameters. The dynamic recrystallization of austenitic grains and the dispersed precipitation of NbCrN particles resulting from the high stress and high temperature in welding, would lead to a improvement of mechanical property of the welded joint. With increasing the distance flom the weld zone to the parent metal, the austenitic grain size gradually increases from -1 μm to - 150 μm, and the microhardness decreases from 301 HV to 225 HV. The tensile strength （about 731 MPa） of the welded joint is comparable to that of the S31042 in the solution-treated state.展开更多
基金financially supported by the National Natural Science Foundation of China(No.51574196)the Aeronautical Science Foundation of China(No.20161125002)the “111 Project”(No.B08040)
文摘In this work, a third generation AI-Li alloy has been successfully spot welded with probeless friction stir spot welding （P-FSSW）, which is a variant of conventional friction stir welding. The Box-Behnken exper-imental design in response surface methodology （RSM） was applied to optimize the P-FSSW parameters to attain maximum tensile/shear strength of the spot joints. Results show that an optimal failure load of 7.83 kN was obtained under a dwell time of 7.2 s, rotation speed of 950 rpm and plunge rate of 30 mm/rain. Sufficient dwell time is essential for heat conduction, material flow and expansion of the stir zone to form a sound joint. Two fracture modes were observed, which were significantly affected by hook defect. In addition to mechanical testing, electron backscattering diffraction （EBSD） and differential scanning calorimetry （DSC） were used for microstructure evolution and property analysis. The precipitation of GP zone and AI3Li as well as the ultrafine grains were responsible for the high microhardness in the stir zone.
文摘The development of microstructure during the aging of Ti-10V-2Fe-3A1 alloy in the 13 and （α＋β） solution-treated and quenched conditions was investigated. The results showed that the isothermal holding below 400℃ yielded homogeneously distributed, spherical ω-phase particles. Fine α aggregates are formed uniformly within 13 grains by nucleating at at particles or β/ω interfaces. At higher temperatures, thin martensite plates decomposed in water-quenched condition. The formation of ω phase was avoided and coarse coarse α-phase plates directly precipitated from the 13 matrix. The highest hardness values were found when the alloys were aged at 400℃ for 8 h. The significance of the observations was discussed in terms of the effect of aging on the precipitations and property.
基金the China National Funds for Distinguished Young Scientists (Grant No. 51325401)the National Natural Science Foundation of China (Granted No. 51474156 and U1660201)the National High Technology Research and Development Program of China (Grant No. 2015AA042504) for grant and financial support
文摘S31042 heat-resistant steel was joined by linear friction welding （LFW） in this study. The microstructure and the mechanical properties of the LFWed joint were investigated by optical microscopy, scanning electronic microscopy, transmission electron microscopy, hardness test and tensile test. A defect-free joint was achieved by using LFW under reasonable welding parameters. The dynamic recrystallization of austenitic grains and the dispersed precipitation of NbCrN particles resulting from the high stress and high temperature in welding, would lead to a improvement of mechanical property of the welded joint. With increasing the distance flom the weld zone to the parent metal, the austenitic grain size gradually increases from -1 μm to - 150 μm, and the microhardness decreases from 301 HV to 225 HV. The tensile strength （about 731 MPa） of the welded joint is comparable to that of the S31042 in the solution-treated state.
