The mold filling and solidification process of a marine propeller hub were simulated using ProCAST. Three casting processes–gravity casting, centrifugal casting and low pressure casting–were compared in order to get the best process. The heat transfer coefficient of the casting/mold interface was determined using a reverse method. The simulated results of velocity, temperature and shrinkage porosity distribution were discussed in detail for the three casting processes. A smooth filling was found in all three casting processes, especially the low pressure casting exhibiting a better filling performance than the other two, but the solidification processes were different. The casting did not experience the sequential solidification, and the feeding paths were blocked, leading to shrinkage porosity defects in the riser and the bottom of the casting in gravity casting and in the upper zone of the casting in low pressure casting. While, the sequential solidification was well controlled in the solidification process of centrifugal casting, and majority of the shrinkage porosity defects can only be observed in the riser. It could be concluded that the centrifugal casting process is the most suitable casting process for the production of propeller hub body. The casting experiments verified the simulation results, and a defect-free propeller hub was obtained by centrifugal casting with a rotational speed of 150 r·min-1.
Wang TongminLi JiaWu LiJie JinchuanCao ZhiqiangKang Huijun
The coarsening process of second-phase droplet in solidifying Al-20 wt% Bi immiscible alloy is in situ studied using synchrotron radiation imaging technology.The collision-induced coarsening and Ostwald coarsening phenomena are directly observed and analyzed.It is found that through observation,collision-induced coarsening phenomenon occurs between droplets with little difference in radius,while Ostwald coarsening phenomenon occurs among droplets with much difference in radius.Moreover,the coarsening rate of Ostwald coarsening is much higher than that of collision-induced coarsening.
Hui-Jun KangPeng ZhouFei CaoJing ZhuYa-Nan FuWan-Xia HuangTi-Qiao XiaoTong-Min Wang
Three-dimensional morphology and formation process of icosahedral quasicrystal phase have been investigated in a melt-spun Al-18 Mn alloy(in wt%).Three distinct layers corresponding to varying temperature gradient have been observed on the cross section of the ribbons.3D morphologies of cellular and dendritic icosahedral phase have been obtained through electro-etching.A model has been proposed to describe the formation process of the icosahedral phase and α-Al during the rapid solidification.The icosahedral phases are primarily precipitated from the melt into fine cellular and dendritic particles,and subsequently engulfed by the α-Al which propagates in a planar morphology.
