| Compared to Al-Ti-B, Al-Ti-C master alloy has a more notable effect on aluminum grain refinement and can avoid the problems of Al-Ti-B master alloy in industrial application. Thus, Al-Ti-C is considered as one of the most promising master alloy. However, poor wettability between graphite and liquid aluminum makes the fabrication of Al-Ti-C difficult, and the fading behavior of the Al-Ti-C also limits its application in industry. Therefore, many attempts have been devoted to find an effective method to prepare Al-Ti-C master alloy in recent years.The paper puts forward a new technice of fabricating Al-Ti-C master alloy and the synthetizing mechanism has also been investigated.The article studied the influence of different parameters on the microstructures of Al-C alloys, then a new Al-C alloy with uniform microstructure was prepared. A new Al-Ti-C master alloy was prepared by utilizing Al-C alloy as carbon source. Meanwhile, the in-situ reaction mechanism of the synthesis TiC particles in Al-Ti-Al4C3melt was built up. The applications of the Al-Ti-C in aluminum alloys were also studied. The major results of the present study are as follows:(1) The influence of different experimental parameters on the microstructures of Al-C alloysAl4C3particles would grow larger with the increase of holding time during the manufacturing process of Al-C alloys. It is thought that small size AI4C3particles would dissolve into the melt and result in the enlargement of Al4C3particles. When the carbon content increases from5wt.%to7wt.%, Al4C3would grow larger. Moreover, the three-dimensional morphologies of Al4C3transforms from hexagonal to plate-like. When the carbon content increases to10wt.%, a large number of graphite powder distribute along grain boundary, and a small quantity of AI4C3phase are formed around the graphite. It is supposed that the Al4C3layer prevents the reaction.(2) The synthesis mechanism of TiC in Al-Ti-Al4C3melts It is found that the TiC particles mainly exhibit a polyhedral shape and agglomerate seriously in the matrix, when they are synthetized by using graphite powder as carbon source. As for the TiC particles synthetized by using Al-5C alloy as carbon source, they exhibit hexagonal platelet and macroporous morphologies, and distribute uniformly in the matrix. It is considered that the different formation mechanism of TiC lead to the great difference. When TiC particles are formed by using Al-5C alloy as carbon source, the reaction mechanism of TiC is solid-liquid reaction process. It is proposed that the dissolved Ti atoms diffuse to AI4C3phase and then TiC particles in-situ synthesize in Al-Ti-Al4C3melts.(3) The fabrication of a new and high efficient Al-Ti-C master alloyA new Al-5Ti-xC(x=0.3-.0.75-,1.25) master alloy was prepared by using Al-5C alloy as carbon source. It is found that with the increase of carbon content, the amount of TiAl3continues to decrease, and the quantity of TiC particles increases rapidly. When carbon content is1.25%, there is no TiAl3phase in the matrix. Compared with the addition of graphite powder as carbon source, a large number of TiC particles with uniform sizes are formed and dispersed in the matrix homogeneously by the new preparation method.(4) The grain refinement and strengthening-toughening for aluminium alloyThe grain refinement and strengthening-toughening for aluminium alloy by the new Al-5Ti-xC(x=0.3、0.75、1.25) master alloys are studied. The microstructures of the aluminium alloys are observed and analysed after grain refinement. Meanwhile, the mechanical properties of the aluminium alloys are tested by using universal material test machine, MM200model wear-resistant testing machine, HR-150a model Rockwell hardness tester. It is found that the Al-5Ti-xC master alloy have excellent grain refining performance and the mechanical properties of the aluminium alloys are improved markedly after grain refinement, compared to the conventional Al-5Ti-1B and Al-5Ti-0.3C master alloys. |
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