The surface composite modification of the 7050 aluminum alloy friction stir-welded joints was performed by shot peening(SP)/multiple rotation rolling(MRR)and MRR/SP,and the fatigue performance of the nugget zone(NZ)wa...The surface composite modification of the 7050 aluminum alloy friction stir-welded joints was performed by shot peening(SP)/multiple rotation rolling(MRR)and MRR/SP,and the fatigue performance of the nugget zone(NZ)was investigated.The results demonstrated that the fatigue life of SP/MRR samples is longer than that of MRR/SP.On the plane 150μm below the surface.The grains with high angle grain boundary account for 71.5%and 34.3%for MRR/SP and SP/MRR samples,respectively.The crack propagation path of the MRR/SP is transgranular and intergranular,and it is intergranular for the MRR/SP.Multitudinous fatigue striations and some voids appeared at the fracture during the stable crack propagation stage.However,fatigue striations for SP/MRR are with smaller spacing,fewer holes,and smaller size under SP/MRR compared with fatigue fracture of MRR/SP.The differences in fatigue properties and fracture characteristics of the NZ are related to the microstructure after the two combined surface modifications.展开更多
Knowledge of transport phenomena and keyhole evolution is important for controlling laser welding process. However, it is still not well understood by far due to the complex phenomena occurring in a wide temperature r...Knowledge of transport phenomena and keyhole evolution is important for controlling laser welding process. However, it is still not well understood by far due to the complex phenomena occurring in a wide temperature range. A transient 3D model including heat transfer, fluid flow and tracking of free surface is built in this study. The transport phenomena are investigated by calculating the temperature and velocity fields. The 3D dynamic keyhole evolution process is revealed through tracking free surface using volume-of-fluid method. The results show that the keyhole deepening speed decreases with laser welding process before the quasi-steady state is reached. The plasma can greatly affect the keyhole depth through absorbing a great amount of laser energy and thus lowering the recoil pressure. Moreover, the relationship between keyhole depth and weld penetration is also discussed. This paper can help to better understand the dynamics in molten pool and then improve laser welding process.展开更多
As a means of surface modification process, metal surface nanocrystallization （MSN） has attracted widespread attention and enjoyed a great prospect. However, currently little research is carried out regarding MSN of...As a means of surface modification process, metal surface nanocrystallization （MSN） has attracted widespread attention and enjoyed a great prospect. However, currently little research is carried out regarding MSN of welded joint. The processes of high energy shot peening （HESP） technology and ultrasonic impact treatment （UIT） were carried out to achieve joint surface nanocrystallization. The grain size of before and after the welded joint surface nanocrystallization were comparatively analyzed with X-ray diffractometer, the surface deformation layer thickness of before and after the welded joint surface nanocrystallization were comparatively analyzed with optical microscopy, the surface hardness of before and after the welded joint surface nanocrystallization were comparatively analyzed with micro hardness machine. The results show that both of the processes can achieve welded joint surface nanocrystaUization and the weld after HESP have smaller grain size, larger deformation layer thickness and higher hardness values than those after UIT. However, HESP is restrained by the shapes and sizes of welding materials, so the UIT process is preferred to use in the general engineering practical applications.展开更多
The power beam processing,including the processing of laser beam,electron beam,ion beam and plasma beam,is one of the advanced modern manufacturing technology,which is extensively used in many fields in the modern ind...The power beam processing,including the processing of laser beam,electron beam,ion beam and plasma beam,is one of the advanced modern manufacturing technology,which is extensively used in many fields in the modern industry.It is playing an important role for modern manufacturing.The weld technique,surface engineering technique and rapid manufacturing technique processed by power beam at BAMTRI are investigated.Some new research progresses are given in this paper.展开更多
The forces acting on a gas tungsten arc （GTA） weld pool are analyzed. A model of static force condition for fullypenetrated weld pool is developed, and the criterion is set up to judge and evaluate the occurrence te...The forces acting on a gas tungsten arc （GTA） weld pool are analyzed. A model of static force condition for fullypenetrated weld pool is developed, and the criterion is set up to judge and evaluate the occurrence tendency of burn-through defect. Transient variations of the forces affecting the surfaces deformation and collapsing of weld pool are computed, and the percentages of their influencing roles are obtained. For specific material and workpiece thickness, the threshold values below which the burn-through phenomenon does not occur are determined, and compared with the experimental results.展开更多
The effect of Fe203 and Liz CO3 additives in flux core on the weld metal oxygen content and weld penetration in self-shielded flux cored arc welding were studied schematically. The result shows that the oxygen content...The effect of Fe203 and Liz CO3 additives in flux core on the weld metal oxygen content and weld penetration in self-shielded flux cored arc welding were studied schematically. The result shows that the oxygen content in the weld metal and weld penetration both increased with the Fe203 addition increased in the range of 5 wt. % to 20 wt. %. The oxygen content in the weld metal was increased with the Li2CO3 addition increased in the range of 1 wt. % to 8 wt. %. However, the weld penetration decreased when Li2CO3 addition exceeding 4 wt. %. High-speed photographic images show that when Fe2O3 addition influx core exceeding 15 wt. %, droplet became excessively large, so that spatters were frequently generated in large numbers. In this study, Fe203 and Li2 CO3 in the amount of 11 wt. % and 4 wt. %, respectively, jointly added in the flux core can achieve a deeper weld penetration with sound usability characteristics.展开更多
基金supported by the National Natural Science Foundation of China(Grants 51865028)the Gansu Provincial Science and Technology Planning Project(Grant No.20YF8GA056).
文摘The surface composite modification of the 7050 aluminum alloy friction stir-welded joints was performed by shot peening(SP)/multiple rotation rolling(MRR)and MRR/SP,and the fatigue performance of the nugget zone(NZ)was investigated.The results demonstrated that the fatigue life of SP/MRR samples is longer than that of MRR/SP.On the plane 150μm below the surface.The grains with high angle grain boundary account for 71.5%and 34.3%for MRR/SP and SP/MRR samples,respectively.The crack propagation path of the MRR/SP is transgranular and intergranular,and it is intergranular for the MRR/SP.Multitudinous fatigue striations and some voids appeared at the fracture during the stable crack propagation stage.However,fatigue striations for SP/MRR are with smaller spacing,fewer holes,and smaller size under SP/MRR compared with fatigue fracture of MRR/SP.The differences in fatigue properties and fracture characteristics of the NZ are related to the microstructure after the two combined surface modifications.
基金Projects(51804348,51804196) supported by the National Natural Science Foundation of China
文摘Knowledge of transport phenomena and keyhole evolution is important for controlling laser welding process. However, it is still not well understood by far due to the complex phenomena occurring in a wide temperature range. A transient 3D model including heat transfer, fluid flow and tracking of free surface is built in this study. The transport phenomena are investigated by calculating the temperature and velocity fields. The 3D dynamic keyhole evolution process is revealed through tracking free surface using volume-of-fluid method. The results show that the keyhole deepening speed decreases with laser welding process before the quasi-steady state is reached. The plasma can greatly affect the keyhole depth through absorbing a great amount of laser energy and thus lowering the recoil pressure. Moreover, the relationship between keyhole depth and weld penetration is also discussed. This paper can help to better understand the dynamics in molten pool and then improve laser welding process.
基金supported by the National Natural Science Foundation(No.50765003)and the National Natural Science Foundation(No.51165026)
文摘As a means of surface modification process, metal surface nanocrystallization （MSN） has attracted widespread attention and enjoyed a great prospect. However, currently little research is carried out regarding MSN of welded joint. The processes of high energy shot peening （HESP） technology and ultrasonic impact treatment （UIT） were carried out to achieve joint surface nanocrystallization. The grain size of before and after the welded joint surface nanocrystallization were comparatively analyzed with X-ray diffractometer, the surface deformation layer thickness of before and after the welded joint surface nanocrystallization were comparatively analyzed with optical microscopy, the surface hardness of before and after the welded joint surface nanocrystallization were comparatively analyzed with micro hardness machine. The results show that both of the processes can achieve welded joint surface nanocrystaUization and the weld after HESP have smaller grain size, larger deformation layer thickness and higher hardness values than those after UIT. However, HESP is restrained by the shapes and sizes of welding materials, so the UIT process is preferred to use in the general engineering practical applications.
文摘The power beam processing,including the processing of laser beam,electron beam,ion beam and plasma beam,is one of the advanced modern manufacturing technology,which is extensively used in many fields in the modern industry.It is playing an important role for modern manufacturing.The weld technique,surface engineering technique and rapid manufacturing technique processed by power beam at BAMTRI are investigated.Some new research progresses are given in this paper.
基金The authors are grateful to the financial support for this project from the National Natural Science Foundation of China under Grant No. 50475131.
文摘The forces acting on a gas tungsten arc （GTA） weld pool are analyzed. A model of static force condition for fullypenetrated weld pool is developed, and the criterion is set up to judge and evaluate the occurrence tendency of burn-through defect. Transient variations of the forces affecting the surfaces deformation and collapsing of weld pool are computed, and the percentages of their influencing roles are obtained. For specific material and workpiece thickness, the threshold values below which the burn-through phenomenon does not occur are determined, and compared with the experimental results.
文摘The effect of Fe203 and Liz CO3 additives in flux core on the weld metal oxygen content and weld penetration in self-shielded flux cored arc welding were studied schematically. The result shows that the oxygen content in the weld metal and weld penetration both increased with the Fe203 addition increased in the range of 5 wt. % to 20 wt. %. The oxygen content in the weld metal was increased with the Li2CO3 addition increased in the range of 1 wt. % to 8 wt. %. However, the weld penetration decreased when Li2CO3 addition exceeding 4 wt. %. High-speed photographic images show that when Fe2O3 addition influx core exceeding 15 wt. %, droplet became excessively large, so that spatters were frequently generated in large numbers. In this study, Fe203 and Li2 CO3 in the amount of 11 wt. % and 4 wt. %, respectively, jointly added in the flux core can achieve a deeper weld penetration with sound usability characteristics.
