Prior to thixoextrusion, the microstructural evolution of semi-solid AM50A magnesium alloy prepared by the recrystallisation and partial remelting (RAP) route was investigated.The effect of compressive ratio on micros...Prior to thixoextrusion, the microstructural evolution of semi-solid AM50A magnesium alloy prepared by the recrystallisation and partial remelting (RAP) route was investigated.The effect of compressive ratio on microstructure of semi-solid AM50A magnesium alloy was studied.Furthermore, tensile properties of thixoextruded components were determined.The results showed that the occurrence of recrystallised grains was closely associated with the location of the first liquid formed above the solidus.With prolonging holding time, deformed microstructure was penetrated, causing fragmentation, which resulted in the decrease of average grain size.Moreover, prolonging holding time was favorable for the improvement of the degree of spheroidization due to the increase in the amount of liquid.With the increase in compressive ratio, the size of solid grain decreased, the degree of spheroidization was improved during partial remelting, and the tensile properties of thixoextruded AM50A components were improved.The tensile properties for AM50A magnesium alloy thixoextruded from starting material produced by the RAP route were better than those of the same alloy produced by die-casting and thixomolding.展开更多
Existing groupwise dimension reduction requires given group structure to be non-overlapped. This confines its application scope. We aim at groupwise dimension reduction with overlapped group structure or even unknown ...Existing groupwise dimension reduction requires given group structure to be non-overlapped. This confines its application scope. We aim at groupwise dimension reduction with overlapped group structure or even unknown group structure. To this end, existing groupwise dimension reduction concept is extended to be compatible with overlapped group structure. Then, the envelope method is ameliorated to deal with overlapped groupwise dimension reduction. As an application, Gaussian graphic model is employed to estimate the structure between predictors when the group structure is not given, and the amended envelope method is used for groupwise dimension reduction with graphic structure. Furthermore, the rationale of the proposed estimation procedure is explained at the population level and the estimation consistency is proved at the sample level. Finally, the finite sample performance of the proposed methods is examined via numerical simulations and a body fat data analysis.展开更多
基金Project(51005217) supported by the National Natural Science Foundation of China
文摘Prior to thixoextrusion, the microstructural evolution of semi-solid AM50A magnesium alloy prepared by the recrystallisation and partial remelting (RAP) route was investigated.The effect of compressive ratio on microstructure of semi-solid AM50A magnesium alloy was studied.Furthermore, tensile properties of thixoextruded components were determined.The results showed that the occurrence of recrystallised grains was closely associated with the location of the first liquid formed above the solidus.With prolonging holding time, deformed microstructure was penetrated, causing fragmentation, which resulted in the decrease of average grain size.Moreover, prolonging holding time was favorable for the improvement of the degree of spheroidization due to the increase in the amount of liquid.With the increase in compressive ratio, the size of solid grain decreased, the degree of spheroidization was improved during partial remelting, and the tensile properties of thixoextruded AM50A components were improved.The tensile properties for AM50A magnesium alloy thixoextruded from starting material produced by the RAP route were better than those of the same alloy produced by die-casting and thixomolding.
基金supported by a grant from the University Grant Council of Hong Kong of ChinaNational Natural Science Foundation of China (Grant No. 11371013)Tian Yuan Foundation for Mathematics
文摘Existing groupwise dimension reduction requires given group structure to be non-overlapped. This confines its application scope. We aim at groupwise dimension reduction with overlapped group structure or even unknown group structure. To this end, existing groupwise dimension reduction concept is extended to be compatible with overlapped group structure. Then, the envelope method is ameliorated to deal with overlapped groupwise dimension reduction. As an application, Gaussian graphic model is employed to estimate the structure between predictors when the group structure is not given, and the amended envelope method is used for groupwise dimension reduction with graphic structure. Furthermore, the rationale of the proposed estimation procedure is explained at the population level and the estimation consistency is proved at the sample level. Finally, the finite sample performance of the proposed methods is examined via numerical simulations and a body fat data analysis.
