Friction stir welding（FSW） was used to weld dissimilar Al-Mg-Si/Al-Zn-Mg aluminum alloys in this work.Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed...Friction stir welding（FSW） was used to weld dissimilar Al-Mg-Si/Al-Zn-Mg aluminum alloys in this work.Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed.Results showed that rather different joint cross sections were obtained when using different sheet configurations.Coarser β＇ phases can be observed at the heat affected zone（HAZ） of the Al-Mg-Si alloy side,which was the main factor affecting the tensile properties and the fatigue properties.Tensile strengths of the dissimilar Al-Mg-Si/Al-Zn-Mg joints using both configurations were higher than that of the Al-Mg-Si FSW joint.When the Al-Zn-Mg alloy was located at the advancing side（AS）,the joints owned better fatigue properties due to the bridging effect of the big secondary phase particles.展开更多
An as-cast Al-Zn-Mg-Sc alloy was friction stir processed varying tool related parameters, yielding microstructures with different grain sizes （0.68, 1.8 and 5.5 μm）. Significant increases in room temperature ductil...An as-cast Al-Zn-Mg-Sc alloy was friction stir processed varying tool related parameters, yielding microstructures with different grain sizes （0.68, 1.8 and 5.5 μm）. Significant increases in room temperature ductility were obtained in these materials with reasonable enhancement in strength. It is demonstrated that the type of microstructure produced by friction stir processing （FSP） has a significant influence on the choice of post-FSP heat treatment design for achieving improved tensile properties. It is also found that the ultrafine grained FSP material could not achieve the desired high strength during the post-FSP heat treatment without grain coarsening, whereas the micro-grained FSP materials could reach such strength levels （〉560 MPa） under conventional age hardening heat treatment conditions.展开更多
The microstructure of as-cast and extruded Mg-14 Li-1 Al-（0, 0.3） La alloys was examined with XRD,OM, SEM, and EDS. The mechanical properties of the extruded specimens with and without La were compared. The results ...The microstructure of as-cast and extruded Mg-14 Li-1 Al-（0, 0.3） La alloys was examined with XRD,OM, SEM, and EDS. The mechanical properties of the extruded specimens with and without La were compared. The results show that La addition has an obvious effect on the microstructure of the as-cast LA141 alloy by reducing the average grain size from 600 to 220 μm. β-Li and LiMgAl2 phases are observed in both alloys, and long-rod-shaped Al2 La phase is also observed in the La containing alloy. After extrusion, Al2 La phases are short-rod-shaped and distribute evenly in the alloy. LAl41-0.3 La alloy has higher elongation（34%）, which is attributed to refined microstructure and weak texture due to shortrod-like Al2 La phase.展开更多
A380 alloy with a relatively thick cross-section of 25 mm was squeeze cast using a hydraulic press with an applied pressure of 90 MPa. Microstructure and tensile properties of the squeeze cast A380 were characterized ...A380 alloy with a relatively thick cross-section of 25 mm was squeeze cast using a hydraulic press with an applied pressure of 90 MPa. Microstructure and tensile properties of the squeeze cast A380 were characterized and evaluated in comparison with the die cast counterpart. Results show that the squeeze cast A380 possesses a porosity level much lower than the die cast alloy, which is disclosed by both optical microscopy and the density measurement technique. The results of tensile testing indicate the improved tensile properties, specifically ultimate tensile strength(UTS: 215.9 MPa) and elongation(Ef: 5.4%), for the squeeze cast samples over those of the conventional high-pressure die cast part(UTS: 173.7 MPa, Ef: 1.0%). The analysis of tensile behavior shows that the squeeze cast A380 exhibits a high tensile toughness(8.5 MJ·m-3) and resilience(179.3 k J·m-3) compared with the die cast alloy(toughness: 1.4 MJ·m-3, resilience: 140.6 k J·m-3), despite that, during the onset of plastic deformation, the strain-hardening rate of the die cast specimen is higher than that of the squeeze cast specimens. The microstructure analyzed by the scanning electron microscopy(SEM) shows that both the squeeze and die cast specimens contain the primary α-Al, Al2 Cu, Al5 Fe Si phase and the eutectic Si phase. But, the Al2 Cu phase present in the squeeze cast alloy is relatively large in size and quantity. The SEM fractography evidently reveals the ductile fracture features of the squeeze cast A380 alloy.展开更多
2D carbon fiber reinforced AZ91 D matrix composites（2D-C_f/AZ91 D composites） were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique（LSEVI）. In order to modify the interface between ...2D carbon fiber reinforced AZ91 D matrix composites（2D-C_f/AZ91 D composites） were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique（LSEVI）. In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon（Py C） coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition（CVD）. Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg_（17）Al_（12） precipitates at the interface. The aluminum improved the infiltration of the alloy and Py C coating protected the fibers effectively. The ultimate tensile strength of 2D-C_f/AZ91 D composites was about 400 MPa. The fracture process of 2D-C_f/AZ91 D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.展开更多
The microstructural evolution and tensile properties of Ti-3Al-8V-6Cr-4Mo-xZr（x = 0,2,4 and 6） titanium alloys were investigated.The precipitated phases and tensile fracture morphologies were observed using scanning...The microstructural evolution and tensile properties of Ti-3Al-8V-6Cr-4Mo-xZr（x = 0,2,4 and 6） titanium alloys were investigated.The precipitated phases and tensile fracture morphologies were observed using scanning electron microscopy and transmission electron microscopy.Experimental results show that the presence of trace impurity Si and the addition of Zr induce the formation of（TiZr）_6Si_3 silicides.The quantity of silicides increases with Zr content increasing.The dispersed silicides refined the grain size of β Zr-containing alloys,and the grain size decreases significantly with Zr content increasing.Accompanying these microstructural changes,the strength of the alloys is enhanced gradually with the increase of Zr content,which is attributed to the combination of precipitation strengthening and grain refinement.展开更多
基金supported by the International S&T Cooperation Program of China(ISTCP) under grant No.2012DFR50580
文摘Friction stir welding（FSW） was used to weld dissimilar Al-Mg-Si/Al-Zn-Mg aluminum alloys in this work.Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed.Results showed that rather different joint cross sections were obtained when using different sheet configurations.Coarser β＇ phases can be observed at the heat affected zone（HAZ） of the Al-Mg-Si alloy side,which was the main factor affecting the tensile properties and the fatigue properties.Tensile strengths of the dissimilar Al-Mg-Si/Al-Zn-Mg joints using both configurations were higher than that of the Al-Mg-Si FSW joint.When the Al-Zn-Mg alloy was located at the advancing side（AS）,the joints owned better fatigue properties due to the bridging effect of the big secondary phase particles.
文摘An as-cast Al-Zn-Mg-Sc alloy was friction stir processed varying tool related parameters, yielding microstructures with different grain sizes （0.68, 1.8 and 5.5 μm）. Significant increases in room temperature ductility were obtained in these materials with reasonable enhancement in strength. It is demonstrated that the type of microstructure produced by friction stir processing （FSP） has a significant influence on the choice of post-FSP heat treatment design for achieving improved tensile properties. It is also found that the ultrafine grained FSP material could not achieve the desired high strength during the post-FSP heat treatment without grain coarsening, whereas the micro-grained FSP materials could reach such strength levels （〉560 MPa） under conventional age hardening heat treatment conditions.
基金Project supported by Natural Science Foundation of Inner Mongolia,China(2015BS0512)
文摘The microstructure of as-cast and extruded Mg-14 Li-1 Al-（0, 0.3） La alloys was examined with XRD,OM, SEM, and EDS. The mechanical properties of the extruded specimens with and without La were compared. The results show that La addition has an obvious effect on the microstructure of the as-cast LA141 alloy by reducing the average grain size from 600 to 220 μm. β-Li and LiMgAl2 phases are observed in both alloys, and long-rod-shaped Al2 La phase is also observed in the La containing alloy. After extrusion, Al2 La phases are short-rod-shaped and distribute evenly in the alloy. LAl41-0.3 La alloy has higher elongation（34%）, which is attributed to refined microstructure and weak texture due to shortrod-like Al2 La phase.
基金supported by the Natural Sciences and Engineering Research Council of Canada and the University of Windsor
文摘A380 alloy with a relatively thick cross-section of 25 mm was squeeze cast using a hydraulic press with an applied pressure of 90 MPa. Microstructure and tensile properties of the squeeze cast A380 were characterized and evaluated in comparison with the die cast counterpart. Results show that the squeeze cast A380 possesses a porosity level much lower than the die cast alloy, which is disclosed by both optical microscopy and the density measurement technique. The results of tensile testing indicate the improved tensile properties, specifically ultimate tensile strength(UTS: 215.9 MPa) and elongation(Ef: 5.4%), for the squeeze cast samples over those of the conventional high-pressure die cast part(UTS: 173.7 MPa, Ef: 1.0%). The analysis of tensile behavior shows that the squeeze cast A380 exhibits a high tensile toughness(8.5 MJ·m-3) and resilience(179.3 k J·m-3) compared with the die cast alloy(toughness: 1.4 MJ·m-3, resilience: 140.6 k J·m-3), despite that, during the onset of plastic deformation, the strain-hardening rate of the die cast specimen is higher than that of the squeeze cast specimens. The microstructure analyzed by the scanning electron microscopy(SEM) shows that both the squeeze and die cast specimens contain the primary α-Al, Al2 Cu, Al5 Fe Si phase and the eutectic Si phase. But, the Al2 Cu phase present in the squeeze cast alloy is relatively large in size and quantity. The SEM fractography evidently reveals the ductile fracture features of the squeeze cast A380 alloy.
基金supported by the National Nature Science Foundation of China (Nos. 51472203, 51521061, 51575447 and 51432008)
文摘2D carbon fiber reinforced AZ91 D matrix composites（2D-C_f/AZ91 D composites） were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique（LSEVI）. In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon（Py C） coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition（CVD）. Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg_（17）Al_（12） precipitates at the interface. The aluminum improved the infiltration of the alloy and Py C coating protected the fibers effectively. The ultimate tensile strength of 2D-C_f/AZ91 D composites was about 400 MPa. The fracture process of 2D-C_f/AZ91 D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.
文摘The microstructural evolution and tensile properties of Ti-3Al-8V-6Cr-4Mo-xZr（x = 0,2,4 and 6） titanium alloys were investigated.The precipitated phases and tensile fracture morphologies were observed using scanning electron microscopy and transmission electron microscopy.Experimental results show that the presence of trace impurity Si and the addition of Zr induce the formation of（TiZr）_6Si_3 silicides.The quantity of silicides increases with Zr content increasing.The dispersed silicides refined the grain size of β Zr-containing alloys,and the grain size decreases significantly with Zr content increasing.Accompanying these microstructural changes,the strength of the alloys is enhanced gradually with the increase of Zr content,which is attributed to the combination of precipitation strengthening and grain refinement.
