Mixed mode Ⅰ/Ⅱ fracture erperiments of LC4-CS aluminum alloy were conductedby using tension--shear specimens with thicknesses of 2, 4, 8 and 14mm. Fracturemechanisms of thickness effect on mixed mode Ⅰ/Ⅱ fracture ...Mixed mode Ⅰ/Ⅱ fracture erperiments of LC4-CS aluminum alloy were conductedby using tension--shear specimens with thicknesses of 2, 4, 8 and 14mm. Fracturemechanisms of thickness effect on mixed mode Ⅰ/Ⅱ fracture were first examined fromfracture surface morphology to correlate with the macroscopic fracture behavior andstress state. It is found that specimen thickness has a strong influence on mixed modefracture. As thickness varies from thin to thick the macroscopic fracture surfacesappear the characteristics of plane stress state (2mm, 4mm--thick specimen), three--dimensional stress state (8mm--thick specimens), and plane strain state (14mm--thickspecimens), respectively. The specimens of all kinds of thicknesses are typical of ten-sile type failure under mode Ⅰ loading condition and shear type failure under mode Ⅱloading condition. Two distinct features coexist on the fracture surfaces under mixedmode loading conditions, and the corresponding proportion varies with loading mix-ity. Void--growth processes are the failure mechanism in both predominately tensile-and shears--type fractures. The size and depth of dimples on the fracture surface varygreatly with thickness. Therefore, it is extraordinary necessary to take into accountthe thickness effect when a mixed mode fracture criterion is being established.展开更多
Diffusion bonding of supcrplastic Al alloy LC4,with prior surface treatment of organic solution protecting coating after electroplishing and stainless steel wool brushing,was performed by Gleeble test machine under co...Diffusion bonding of supcrplastic Al alloy LC4,with prior surface treatment of organic solution protecting coating after electroplishing and stainless steel wool brushing,was performed by Gleeble test machine under conditions ranged 490—530 ℃,1.0—3.0 MPa. 30—180 min and vacuum of 1.0×10^(-3) Pa.The joints were examined to have similar strength and microstructure to the base metal Discussion was made on the effect of superplastic treatment on bonding.The micromechanism for diffusion bonding of super- plastic metal was suggested as the migration of original bond interfaces caused by atomic diffusion and grain growth. Experimental results for the alloy as quench-aged state were presented to compare with the superplastic one.展开更多
The effect of SIMA process parameters on LC 4 alloy’s microstructure and the microstructural evolution of various soaking times have been studied. The results show that effective strain in cold deformation before reh...The effect of SIMA process parameters on LC 4 alloy’s microstructure and the microstructural evolution of various soaking times have been studied. The results show that effective strain in cold deformation before reheating has a great influence on microstructural evolution. Grain size decreases and its shape also approaches to sphericity with increasing effective strain. The amount of liquid phase increases at grain boundaries and grain shape becomes smooth with increasing heating temperature. The main mechanism of grain coarsening is coalescence when eutectic liquid is rare and not totally distributed at all boundaries. Otherwise the main mechanism of grain coarsening is Ostwald ripening and the connection coarsening is more difficult to perform when the regions are nearly full of eutectic liquid.展开更多
The mechanical behavior of LC 4 alloy in the semisolid state at high volume fractions of solid has been studied through unconstrictive compressing test. The results show that peak stress mainly depends on grain bound...The mechanical behavior of LC 4 alloy in the semisolid state at high volume fractions of solid has been studied through unconstrictive compressing test. The results show that peak stress mainly depends on grain boundary’s cohesion and instantaneous strain rate sensitivity in the semisolid state, which is similar to that in the solid state. Analyses on microstructures and status of compressive stress of specimen demonstrate that segregation of liquid solid phase is mainly affected by strain rate and deformation temperature. There are mainly two kinds of flow in liquid phase: either from the region with relatively large hydrostatic compressive stress to the region with relatively small hydrostatic compressive stress or from the grain boundaries perpendicular to the compression axis to the grain boundaries with a certain directional angle to the compression direction. Based on the above results, compressive deformation mechanism mainly depends on deformation temperature, strain rate and stress state.展开更多
On the bases of high temperature creep experiments, the research on engineering application of rheological forming is carried out on two kinds of light metal alloy parts named cylindrical shell of Lc4 aluminum alloy a...On the bases of high temperature creep experiments, the research on engineering application of rheological forming is carried out on two kinds of light metal alloy parts named cylindrical shell of Lc4 aluminum alloy and vane disk with complex curved surface of TC11 titanium alloy. Moreover, the mechanical property tests under room and high temperatures for the workpieces produced by this new technique are also done, the results showed that they are much improved evidently compared with those produced by traditional method.展开更多
文摘Mixed mode Ⅰ/Ⅱ fracture erperiments of LC4-CS aluminum alloy were conductedby using tension--shear specimens with thicknesses of 2, 4, 8 and 14mm. Fracturemechanisms of thickness effect on mixed mode Ⅰ/Ⅱ fracture were first examined fromfracture surface morphology to correlate with the macroscopic fracture behavior andstress state. It is found that specimen thickness has a strong influence on mixed modefracture. As thickness varies from thin to thick the macroscopic fracture surfacesappear the characteristics of plane stress state (2mm, 4mm--thick specimen), three--dimensional stress state (8mm--thick specimens), and plane strain state (14mm--thickspecimens), respectively. The specimens of all kinds of thicknesses are typical of ten-sile type failure under mode Ⅰ loading condition and shear type failure under mode Ⅱloading condition. Two distinct features coexist on the fracture surfaces under mixedmode loading conditions, and the corresponding proportion varies with loading mix-ity. Void--growth processes are the failure mechanism in both predominately tensile-and shears--type fractures. The size and depth of dimples on the fracture surface varygreatly with thickness. Therefore, it is extraordinary necessary to take into accountthe thickness effect when a mixed mode fracture criterion is being established.
文摘Diffusion bonding of supcrplastic Al alloy LC4,with prior surface treatment of organic solution protecting coating after electroplishing and stainless steel wool brushing,was performed by Gleeble test machine under conditions ranged 490—530 ℃,1.0—3.0 MPa. 30—180 min and vacuum of 1.0×10^(-3) Pa.The joints were examined to have similar strength and microstructure to the base metal Discussion was made on the effect of superplastic treatment on bonding.The micromechanism for diffusion bonding of super- plastic metal was suggested as the migration of original bond interfaces caused by atomic diffusion and grain growth. Experimental results for the alloy as quench-aged state were presented to compare with the superplastic one.
文摘The effect of SIMA process parameters on LC 4 alloy’s microstructure and the microstructural evolution of various soaking times have been studied. The results show that effective strain in cold deformation before reheating has a great influence on microstructural evolution. Grain size decreases and its shape also approaches to sphericity with increasing effective strain. The amount of liquid phase increases at grain boundaries and grain shape becomes smooth with increasing heating temperature. The main mechanism of grain coarsening is coalescence when eutectic liquid is rare and not totally distributed at all boundaries. Otherwise the main mechanism of grain coarsening is Ostwald ripening and the connection coarsening is more difficult to perform when the regions are nearly full of eutectic liquid.
文摘The mechanical behavior of LC 4 alloy in the semisolid state at high volume fractions of solid has been studied through unconstrictive compressing test. The results show that peak stress mainly depends on grain boundary’s cohesion and instantaneous strain rate sensitivity in the semisolid state, which is similar to that in the solid state. Analyses on microstructures and status of compressive stress of specimen demonstrate that segregation of liquid solid phase is mainly affected by strain rate and deformation temperature. There are mainly two kinds of flow in liquid phase: either from the region with relatively large hydrostatic compressive stress to the region with relatively small hydrostatic compressive stress or from the grain boundaries perpendicular to the compression axis to the grain boundaries with a certain directional angle to the compression direction. Based on the above results, compressive deformation mechanism mainly depends on deformation temperature, strain rate and stress state.
基金supported by the National Personnel Department for returned talents(lincaipeizi[2001]30#)the Education Ministry of China for the university with doctoral discipline (No. 200805380004)
文摘On the bases of high temperature creep experiments, the research on engineering application of rheological forming is carried out on two kinds of light metal alloy parts named cylindrical shell of Lc4 aluminum alloy and vane disk with complex curved surface of TC11 titanium alloy. Moreover, the mechanical property tests under room and high temperatures for the workpieces produced by this new technique are also done, the results showed that they are much improved evidently compared with those produced by traditional method.
