Underwater friction stir welding of 2219 aluminum alloy was carried out in order to further improve the joint performances by varying welding temperature history.The results indicated that the tensile strength of the ...Underwater friction stir welding of 2219 aluminum alloy was carried out in order to further improve the joint performances by varying welding temperature history.The results indicated that the tensile strength of the joint can be improved from 324 MPa by external water cooling action in normal to 341 MPa.However,the plasticity of the joint is deteriorated.The underwater joint tends to fracture at the interface between the weld nugget zone and the thermal mechanically affected zone on the advancing side during tensile test,which is significantly different from the normal joint.展开更多
Extensive bleaching of Montastrea annularis spp. group and several other scleractinian taxa occurred on the reefs within the Arrecifes de Cozumel National Park of Cozumel, Mexico, after the passage of Hurricane/Tropic...Extensive bleaching of Montastrea annularis spp. group and several other scleractinian taxa occurred on the reefs within the Arrecifes de Cozumel National Park of Cozumel, Mexico, after the passage of Hurricane/Tropical Storm Rina. We conducted six drift dives at five different dive sites （-13 h of scuba diving） and photographed a variety of reefs scenes at depths of 10-28 m. Bleaching was noted at depths of 10-40 m in a variety of scleractinian species, including M. annularis species group, especially M. faveolata and Siderastrea siderea. Considering that local dive guides had not observed bleaching prior to the storm and the sea surface temperature did not exceed the local bleaching threshold, it is probable that the extensive rainfall associated with Hurricane/Tropical Storm Rina lowered salinity sufficiently via subsurface freshwater springs to cause bleaching in susceptible species. This suggests the need to monitor not only subsurface sea temperature but also subsurface salinity in localities where freshwater springs occur adjacent to or within coral reefs.展开更多
The superplastic forming of Ti alloy welds has great application prospects in producing integrated components. However, the nugget zone（NZ） of the Ti alloy welds,produced by fusion welding or conventional friction s...The superplastic forming of Ti alloy welds has great application prospects in producing integrated components. However, the nugget zone（NZ） of the Ti alloy welds,produced by fusion welding or conventional friction stir welding（FSW）, consists of lamellar micro structure, which exhibits either low superplasticity or high superplastic temperautre and low strain rate. As a result, the NZ plays a leading role in hindering the superplastic forming of the whole welds.In this study, submerged friction stir welding（SFSW） was conducted in Ti-6Al-4 V alloy for the first time, and a defectfree weld with the NZ consisting of a strip microstructure was obtained. The NZ exhibited a low-temperature superplasticity at 600℃, which was the lowest superplastic temperature ever reported in the Ti alloy welds. Besides, at 800℃, the NZ showed high strain rate（3×10^（-2） s^（-1）） superplasticity and a largest elongation of 615% at 1×10^（-3） s^（-1）. Compared to conventional FSW joints, the NZ of SFSW joint exhibited a much lower flow stress and a decrease in optimal superplastic temperature by 100℃. This is mainly attributed to the easy globularization of the strip microstructure, enhancing the ability of grain/phase boundary sliding.展开更多
基金Project (2010CB731704) supported by the National Basic Research Program of ChinaProject (2006BAF04B09) supported by the NationalKey Technology Research and Development Program of ChinaProject supported by the Program of Excellent Team in Harbin Instituteof Technology,China
文摘Underwater friction stir welding of 2219 aluminum alloy was carried out in order to further improve the joint performances by varying welding temperature history.The results indicated that the tensile strength of the joint can be improved from 324 MPa by external water cooling action in normal to 341 MPa.However,the plasticity of the joint is deteriorated.The underwater joint tends to fracture at the interface between the weld nugget zone and the thermal mechanically affected zone on the advancing side during tensile test,which is significantly different from the normal joint.
文摘Extensive bleaching of Montastrea annularis spp. group and several other scleractinian taxa occurred on the reefs within the Arrecifes de Cozumel National Park of Cozumel, Mexico, after the passage of Hurricane/Tropical Storm Rina. We conducted six drift dives at five different dive sites （-13 h of scuba diving） and photographed a variety of reefs scenes at depths of 10-28 m. Bleaching was noted at depths of 10-40 m in a variety of scleractinian species, including M. annularis species group, especially M. faveolata and Siderastrea siderea. Considering that local dive guides had not observed bleaching prior to the storm and the sea surface temperature did not exceed the local bleaching threshold, it is probable that the extensive rainfall associated with Hurricane/Tropical Storm Rina lowered salinity sufficiently via subsurface freshwater springs to cause bleaching in susceptible species. This suggests the need to monitor not only subsurface sea temperature but also subsurface salinity in localities where freshwater springs occur adjacent to or within coral reefs.
基金supported by the National Natural Science Foundation of China under Grant(51471171,51601194,and 51331008)
文摘The superplastic forming of Ti alloy welds has great application prospects in producing integrated components. However, the nugget zone（NZ） of the Ti alloy welds,produced by fusion welding or conventional friction stir welding（FSW）, consists of lamellar micro structure, which exhibits either low superplasticity or high superplastic temperautre and low strain rate. As a result, the NZ plays a leading role in hindering the superplastic forming of the whole welds.In this study, submerged friction stir welding（SFSW） was conducted in Ti-6Al-4 V alloy for the first time, and a defectfree weld with the NZ consisting of a strip microstructure was obtained. The NZ exhibited a low-temperature superplasticity at 600℃, which was the lowest superplastic temperature ever reported in the Ti alloy welds. Besides, at 800℃, the NZ showed high strain rate（3×10^（-2） s^（-1）） superplasticity and a largest elongation of 615% at 1×10^（-3） s^（-1）. Compared to conventional FSW joints, the NZ of SFSW joint exhibited a much lower flow stress and a decrease in optimal superplastic temperature by 100℃. This is mainly attributed to the easy globularization of the strip microstructure, enhancing the ability of grain/phase boundary sliding.
