Study On The TiC Particle Size Distribution And Formation Mechanism Of Ti-Rich Zone On The TiC Surface In Al-Ti-C Master Alloys

The influence factors on the size distribution of TiC particles in Al-Ti-C alloys and the formation mechanism of Ti-rich layer between TiC and aluminum melt were studied by X-ray Diffraction (XRD), Optical Micrograph (OM), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM) and Field Emission Scanning Electron Microscopy (FESEM), etc. Several works were included in this paper:(1) TiC particles will grow larger with the increase of melting temperature and the extension of melting time during the manufacturing process of Al-Ti-C master alloys. It is thought that small size TiC particles will re-dissolve into the aluminum melt in the high temperature melt, leading to the increase of C concentration. During the cooling process, dissolved C and Ti will precipitate on the surface of nucleated TiC particles, leading to the enlargement of TiC particles.However, mass transport is getting more and more difficult with the decrease of temperature. Dissolved carbon and titanium are not able to diffuse to the surface of nucleated TiC particles in some zone of the low temperature melt, sothat they could only precipitate out as micro size TiC particles. Therefore, micro size TiC particles will appear in the Al-Ti-C master alloys which were manufactured at high temperature. For instance, the polarization of TiC particle size will appear in the Al-Ti-C master alloy manufactured at 1700℃.(2) Al-Ti-C master alloys manufactured at 1300℃and 1700℃could both increase the tensile strength of ZL203. But the strenghthen efficiency is different. The tensile strength of ZL203 will increase if the addition amount of Al-Ti-C master alloy manufactured at 1300℃increases, and 245MPa was achieved when the addition amount is 1.0%. However, Al-Ti-C master alloy manufactured at 1700℃has better strenghthen efficiency, the tensil strength could be more than 255MPa when the addition amount is about 0.4%. Al-Ti-C master alloy manufactured at 1700℃has more active particles and the polarization of particle size is enormous. The micro size particles results in the dispersion of TiC particles, leading to the better strenghthen efficiency.(3) The titanium equilibrium between TiCx and aluminum melt was calculated via thermodynamic analysis. The relation between C content in TiCx and the Ti concentration on the interface was researched, providing the the balanceable titanium concentration on the interface of TiCx. The calculation result indicates that Ti will aggregrate on the surface of TiCx and result into the formation of Ti-rich zone when the C content is low in TiCx. And the Ti concentration will increase with the decreases of carbon content in TiCx. Titanium atoms in high titanium concentration zone are not able to diffuse around during rapid solidification process, so they just precipitate as Ti3A1.