Synthesis Of AlTiC Under Ultrasonic Field And Research On Novel Al-Mg-Si Alloys

Based on the demand for low-cost AlTiC alloys and benefited fromresearch work of my predecessors, an innovative method was designed forpreparing AlTiC master alloy under ultrasonic field as well as low melttemperature (1073K-1173K), using 99.7% commercial alloy, graphite andK2TiF6. The introduction of ultrasonic vibrations into melt facilitates thesynthesis process of AlTiC and disperses the agglomeration groups composedby TiC particles. The preparation process of AlTiC master alloy wasinvestigated by SEM with EDS. The effectiveness of ultrasonic field wasconfirmed by the comparison of grain refining efficiency of 99.8%commercial aluminum. Also, experiment results indicate that direct reactionbetween Carbon and K2TiF6 dominated the TiC synthesis process compared toother reaction models.Towards to the further improvement of refining ability, the AlTiCfabrication process was optimized through the control of graphite amount andsize, because C addition has been proved to be crucial for this synthesisprocess. Analysis was performed on the influence of graphite size andamount.Part of thesis was focused on the effect of alloy composition onprecipitates of the Al-Mg-Si alloys refined by AlTiC. The influence of Si, Mg,Mn, Cr additions on alloy microstructure and properties was analyzed usingTEM and HRTEM. The crystal structures of precipitates in Al-Mg-Si alloyswere determined by selected area diffraction pattern and fast Fouriertransforms pattern. The precipitation sequence of various kinds of metastablephases in Al-Mg-Si alloy was discussed.