Preparation And Characterization Of C_p/AZ91D Composites

In thesis,Cp/AZ91D magnesium matrix composites were successfully prepared by vibration composite casting method.In the early stage,mechanical vibration method was used to optimize the as-cast AZ91D by changing vibration frequency and mold temperature parameters,and the influence of different vibration frequency and mold temperature on the microstructure and mechanical properties of AZ91D was studied to obtain the optimal parameters.This parameter was then applied to the preparation of Cp/AZ91D magnesium matrix composite,and the Cp/AZ91D magnesium matrix composite with Cp dispersion distribution was successfully obtained.The distribution of Cp in Cp/AZ91D under different process conditions and the solidification process and mechanism of Cp/AZ91D were studied.The effect of holding temperature and holding time on Cp/AZ91D semi-solid microstructure was studied.The effects of holding temperature and holding time on the microstructure and tensile properties of thixotropic Cp/AZ91D were studied.（1）By studying the influence of different heating temperature and heating time parameters on semi-solid Cp/AZ91D magnesium matrix composites,the optimal semi-solid process was obtained:600℃ holding temperature,1h holding time.With the increase of the holding temperature or the extension of the holding time,the liquid phase content of the material gradually increases,and the black spot-like phase in the material grain gradually increases,and the spheroidization effect is gradually obvious.However,higher holding temperature or longer holding time will lead to too much liquid phase content of the material,and the coarsening effect is gradually obvious.The fundamental reason for these phenomena is that the expansion capacity of atoms increases with the increase of temperature.The optimum semi-solid microstructure can be obtained when the holding temperature is 600℃ and the holding time is 1h.The thixotropic test of the samples also showed that the best properties of the materials were obtained at 600℃ and 1h,with tensile strength of 307MPa and elongation of 12.6%.With the increase of holding temperature and the extension of holding time,the tensile strength and elongation of the material showed a trend of first increasing and then decreasing.（2）By studying the influence of different temperature and time parameters on the semi-solid Cp/AZ91D structure,the optimal semi-solid process was obtained:600℃temperature and 1h time.With the increase of the holding temperature or the extension of the holding time,the liquid phase content of the material gradually increases,and the black spot-like phase in the material grain gradually increases,and the spheroidization effect is gradually obvious.However,higher holding temperature or longer holding time will lead to too much liquid phase content of the material,and the coarsening effect is gradually obvious.The fundamental reason for these phenomena is that the expansion capacity of atoms increases with the increase of temperature.The optimum semi-solid microstructure can be obtained when the holding temperature is 600℃ and the holding time is 1h.The thixotropic test of the samples also showed that the best properties of the materials were obtained at 600℃ and 1h,with tensile strength of 307MPa and elongation of 14.9%.With the increase of insulation temperature and the extension of insulation time,the tensile strength of the material first increases and then decreases,and the elongation of the material also shows a trend of first increasing and then decreasing.（3）Contrast gravity casting Cp/AZ91D composite,vibration casting Cp/AZ91D composite and thixotropic Cp/AZ91D composite.Compared different preparation of composite material technology,normal gravity casting Cp/AZ91D composite material obtained by coarse grains,grain size reduced significantly after the vibration casting,but will introduce volume defects such as gas,adopt touch into technology of grain size and grain size after the vibration casting after fairly,but due to the increasing material feeding performance,Material defects are greatly reduced.In view of the above reasons,Cp/AZ91D prepared by thixoforming process has the best tensile strength of 307MPa and elongation of 14.9%.