The Synthesis Of N-Doped TIC_x Nucleation Agent And Its Effect On The Properties Of Aluminum Alloys

Through grain refinement to achieve small and uniform equiaxed grain structure is one of the important means to improve the comprehensive properties of aluminum ingots, while adding grain refinement agent is the most simple and effective method. Many studies have proved that Al-Ti-C master alloy can avoid the problems during the application of Al-Ti-B master alloy. Meanwhile, Al-Ti-C is considered to be one of the most promising master alloys in industrial application. However, the poor wettability between graphite and liquid aluminum, the instability of TiCx and fading behavior restricts its industrial production and further application.TiCx is a kind of non-stoichiometry compound that have face-centered cubic structure and the C/Ti atomic ratio can change between0.47-0.98while still maintain a certain crystal structure. Many carbon vacancies exist in TiCx lattice structure and influence the structural stability seriously which result in its evolution at low temperature. Taking advantage of the carbon vacancies in TiCx, the present work chooses different nitrogen source to prepare TiCx particles with N atoms. The influence of various experimental parameter on microstructure has also studied. A kind of aluminum grain refiner with N-doped TiCx and TiB2particles has been fabricated. It is found that C element has an important effect on the reaction process of the Al-Ti-C-B-N system. Eventually, the prepared master alloy has been used to improve the mechanical properties of aluminum alloys.The main research contents in the present paper are as follows:(1) The influence of nitrogen source on the synthesis of N-doped TiCx particlesUsing N2as nitrogen source, lots of A1N particles are formed in the process without N-doped TiCx particles. When using Mg3N2and BN as the initial source, both of the prepared TiCx particles have N element, and BN can provide N and B at the same time. As a result, N-doped TiCx and TiB2particles have been fabricated. Therefore, BN is comparatively more optimized nitrogen source. (2) Effect of preparation parameters on Al-Ti-C-B-N master alloyBall milling is of vital importance to the fabrication of master alloys. The microstructure of the prepared alloys after ball milling for4h is similar to that without ball milling, and most of the particles are about2μm-5μm. When the ball milling time increase to8h, the size of the particles decreased to0.2μm-0.5μm and uniformly distribute on the aluminum matrix. If further extending the time of ball milling to16h, it will generate a lot of particles about100nm and the particles easily aggregate in the alloy. The composition of an alloy also plays a key role on the microstructure. When the BN content is1%, the microstructure is optimal and the trace amount of N is detected in TiCx particles. The TiCx particles exhibit an octahedron and irregular polyhedron shape. The morphology of TiB2particle is hexagon plate-like and its size is about1μm-2μm.(3) The role of carbon on the reaction of Al-Ti-B-N systemAdding graphite into Al-Ti-B-N system has a remarkable effect on the reaction mechanism and final product. The main phases are A1N and A1B2with a small amount of TiB2. After adding0.1%graphite, the reaction process releases large amount of heat and promote the direct reaction between Ti and BN. Finally, lots of TiCx particles and TiB2particles with trace N are synthesized.(4) The grain refinement and improvement of mechanical properties by master alloysThe grain refinement and strengthening-toughing behaviors of self-made master alloy on commercial pure aluminum, Al-5Cu and Al-5Mg have been studied in this paper. The mechanical properties of the alloys are tested by universal tensile testing machine, MM200wear tester and Brinell hardness tester. CHI660E electrochemical workstation is used to detect the corrosion resistance of A1-5Mg alloy. The research results show that the self-prepared master alloy has a good refining effect on aluminum alloys and exellent decline resistance. It can improve the comprehensive mechanical properties remarkably which is better than the current Al-Ti-B and Al-Ti-C maser alloy.