Lu Dehong

Process Condition Effects on Gelatination Kinetics in a Silica Sol Ceramic Mold

To shorten the preparation period of a silica sol ceramic mold, this paper studied the influence of the process conditions on silica sol-based ceramic gelatination kinetics, such as the presence of the sand sleeves, the thickness of the ceramic mold, the gelatination temperature, and the atmospheric pressure. The results show that, the initial gelatination speed of the ceramic slurry is fast without sand sleeves, however, the change in the final gelatination time is little. The thicker the sand sleeves, the slower the slurry gelatination. The gelatination reaction speed increased linearly with the gelatination temperature, and the final gelatination time was 10 minutes at all of the temperatures tested. Compared with the atmospheric pressure, when the vacuum level was −0.01MPa (1.45 psi), the slurry gelatination increased significantly faster, but when the vacuum level increased more than −0.01MPa (1.45 psi), the slurry gelatination velocity decreased. Therefore, the optimum vacuum level for gelatination was found to be −0.01MPa (1.45 psi). This paper analyzes the process for the gelatination and the effects/causes of each factor.

STUDY OF ROLLING-REMELTING SIMA PROCESS FOR PREPARING THE SEMI-SOLID BILLET OF ZCuSn10 ALLOY

Semi-solid billet of ZCuSn10 alloy is prepared by strain induced melt activation(SIMA) method which included the rolling and remelting process. Firstly, ZCuSn10 alloy is cast, and samples are cut from ingot casting. Secondly, the samples are rolled with 2~4 passes after holding at 450 ℃ for 15 min, then the new samples are cut from deformed alloy. Lastly, the new samples are reheated up to 850 ℃ or 875 ℃ for 15 min, then water quenching. Semi-solid microstructure is observed and compared with microstructure of ZCuSn10 alloy directly reheated after casting. The distribution of Sn element in microstructure under different conditions is measured by using EDS function of SEM, and the microstructure changes during the SIMA process are observed by means of OM and TEM. Based on the experiments, the microstructure evolution is synthetically analyzed and explained during the course of semi-solid billet of ZCuSn10 alloy prepared by SIMA method. The results indicate that semi-solid microstructure of ZCuSn10 alloy by rolling- remelting SIMA process is equal-fine grain, and spheroidization of solid particle is well. The optimum semi- solid microstructure is obtained when alloy deformed 19.7% is remelted at 875 ℃ for 15 min, the average grain diameter is 75.8 μm, shape factor is 1.62, and volume fraction of liquid phase is 17.28%. Deformation process plays a crucial role in grain refinement and spheroidization during SIMA process for preparing the semi-solid billet of ZCuSn10 alloy, as deformation and remelting temperature increases, the size and shape of solid phase in semi solid microstructure are smaller and more round, volume fraction of liquid phase increases. The main mechanism of SIMA process preparing semi-solid billet of ZCuSn10 alloy is that predeformation breaks dendrites and stores energy of deformation into dendrites, and promotes dendrites melting through remelting process. Meanwhile, liquid phase occupies sharp corners of solid particles by Sn element diffusing from liquid phase into a solid phase, so that fine, uniform and roundness a solid particles are gained.