Abstract

One of the most important technical barriers that hinders the development and implementation of nanoparticulate reinforced aluminium alloys is the difficulty to avoid the formation of clusters and to obtain their homogeneous distribution. The present work summarises the results obtained with the use of an ultrasound probe that was immersed into the melt alloy containing nanodiamond particulates just before the casting step. The microstructure and tensile properties of the obtained specimens are compared with nanoreinforced samples obtained with conventional stir cast process. The materials used in the study are the Al-Si7Mg0.6 casting alloy and nanodiamond particulates obtained by detonation synthesis. Samples containing up to 0.5 wt.% of nanodiamonds have been obtained. The use of the ultrasound probe results in the elimination of nanoparticulate clusters and provides an improvement of mechanical properties in comparison to properties measure with the unreinforced alloy and also with the conventionally stir cast composite.

Abstract

Disturbance of the molten metal flow during ladle pouring before the plunger advancing in the aluminium alloy die casting process can cause entrapment defects of air and oxide film. Slow pouring to control the turbulence of the flow front reduces productivity due to increased cycle time. Further, the risk of cold flake formation increases caused by large temperature drops in accordance with the long cycle time. On the other hand, rapid pouring is desired to improve productivity, but the risk of air entrapment increases. Therefore, quick and quiet pouring is desired in the ladle pouring process. In the present study, we focus on variable tilting speed as a method to achieve good ladle pouring. The effects of variable ladle tilting speed and switching time on the wave behavior of molten metal are investigated in visualization experiments and simulations. The flow behaviours in ladle pouring are simulated using ”COLMINA CAE”, which is the casting analysis software by particle-based SPH method. Furthermore, the plunger advancing process is also examined. From the simulation results, the variable tilting speed from fast to low can suppress the rise of the maximum wave height of molten aluminium alloy. However, the pouring completion time is longer. Further, the falling position of molten metal poured from the ladle varied with changing tilting speed. And then, the wave height is influenced not only by ladle pouring but also by the plunger advancing process. These trends of wave behaviour obtained in the simulation are similar to that of the actual phenomenon. Therefore, the present simulation method can accurately estimate the ladle pouring process and plunger advancing process. So, casting CAE is an effective tool for exploring die casting conditions.