The Research On Stability And Rheological Property Of ZL117 Alloy Semi-solid Slurry

The semi-solid rheocasting is a hot research subject in the domestic and international academe presently, and the research on the semi-solid slurry's stability and rheological property is crucial for the semi-solid rheocasting.The main content of this thesis involves three aspects: first, researching the microstructure changes of the semi-solid slurry hold in different temperatures for different time;second, researching the changes of the rheological property of the semi-solid slurry;third, designing an equipment for isothermal holding and rationing for semi-solid slurry.The results of the semi-solid slurry isothermal holding experiment show that only in the condition of 650℃, 640℃, 630℃ , 620℃ or 610℃ isothermal holding, with the increasing of isothermal holding time, the volume fraction of the solid phase keep steady in the main, but the average equivalent diameter of primary silicon particles increases obviously, the increase speed is lower before 15 minutes, and faster after 15 minutes. The main reason of the change in the equivalent diameter of primary silicon particles is that the percentage of the smallness diameter primary silicon particles diminishes gradually, and the percentage of the big diameter primary silicon particles increases gradually. At the same time, the shape coefficient of the primary silicon particles increases slowly before 15 minutes, then enlarges suddenly and diminishes after the 15 minutes.With the isothermal holding temperature increasing, the volume fraction of solid phase and the equivalent diameter of primary silicon particles in the semi-solid slurry increase gradually, the shape coefficient of the primary silicon particles becomes larger, in other words, the quality of the semi-solid slurry turns worse. The results of the experiment have provided the basis for choosing the isothermal holding to the semi-solid slurry.The experiment which tested the semi-solid slurry's rheological property showsthat in the condition of continuous cooling, the instant apparent viscosity will increase when the solid phase fraction of the semi-solid slurry increases. Increasing the intensity of the stirring and diminishing cooling rate can reduce the instant apparent viscosity of the ZL117 alloys. In the condition of isothermal stirring up, as the solid phase fraction becoming high, the instant apparent viscosity will become high when the stirring begin, and the result is that steady apparent viscosity also becomes high finally. As the cooling rate becomes low, the steady apparent viscosity becomes low;and as the intensity of the stirring increasing, the steady apparent viscosity has a change process that first becomes low and then becomes high. When the intensity of the stirring approaches to 14A, the steady apparent viscosity is the least value. According to the experiment results, when choosing the semi-solid slurry's preparation and isothermal holding, the isothermal holding temperature should choose the high parameter, the cooling rate should choose the low parameter, and the intensity of the stirring parameter should be near to 14A. In this parameters, the fluidity and the forming ability of the semi-solid slurry is best.Basing on the need of rationing the semi-solid slurry continues for industrialization of the recasting, a suit of isothermal holding and rationing system has been designed, this system can realize the function of depositing, isothermal holding and rationing clankingly.