Preparation Technical Of In-Situ TiB₂ And Mg₂Si Particulate Reinforced Al Matrix Composites

The in-situ preparation of aluminum-matrix composites has a huge advantage compared to the traditional particle adding methods from air. TiB2 particles have high melting point, high hardness and elastic modulus and many other advantages; however, it's difficult to solve the problem that the volume fraction of in-situ TiB2 particle in Al-matrix composite is low. The Mg2 Si has high melting point, high modulus of elasticity, low density, high hardness and low thermal expansion coefficient, so it is suitable for aluminum matrix composites to be the reinforcement. The Mg2 Si phase which looks like Chinese script morphology and the brittle eutectic matrix of the composite lower the ductility and limit the reinforcement effects. In-situ TiB2 aluminum-matrix composites were prepared by the salt-metal reactions, then in-situ TiB2+Mg2Si aluminum-matrix composites were prepared with alloy smelting, and it is compared with the modification effect of rare earth and rare earth & phosphorus on Mg2 Si. The mechanical properties of these three materials were also compared. The mechanical properties of composite materials were analyzed.In-situ 5vol%TiB2/Al-2Mg aluminum-matrix composites were prepared by the salt-metal reactions using two salts of K2TiF6 and KBF4. And in-situ 5vol%TiB2/Al-4.5Cu-2Mg aluminum-matrix composites were also prepared by this way. The morphology, composition, particle size and distribution, tensile properties and hardness of these aluminum-matrix composites were analyzed and tested with the help of optical microscope, FSEM, X-ray diffraction, tensile test machine, hardness tester, etc. The results show that TiB2 particles are uniformly distributed in the matrix without large agglomerations. The size of TiB2 particles is measured to be under 0.4?m in diameter. Some TiB2 particles are gathering along the grain boundary regions. The ultimate tensile strength and yield stress of the in-situ TiB2/Al-4.5Cu-2Mg matrix composite are respectively improved by 26.15% and 27.71% in comparison with the matrix alloy. With the help of mechanical stirring, the size, distribution, agglomerations of the particles and the properties of aluminum-matrix composites have been further optimized.In-situ TiB2 aluminum-matrix composites were prepared by the salt-metal reactions, then Mg2 Si phase were synthesized with alloying, and it is compared with the modification effect of 0.5% rare earth and 0.5% rare earth & 0.2%phosphorus on Mg2 Si. The results show that the refining effects of TiB2 on Mg2 Si were much better than the other two methods. The Mg2 Si phase is refined from Chinese script morphology to short dispersed sticks by TiB2 particles, and pseudo eutectic microstructure reduced generously. The Mg2 Si particles are refined from above 50?m to under 10?m in size. The interface and heterogeneous nucleation of TiB2 and Mg2 Si is analyzed, and the disregistry of TiB2 and Mg2 Si is less than 5%, so they are completely coherent relationship, which indicates that TiB2 can be the nuclei of the Mg2 Si phase. The yield stress and ultimate tensile strength of the in-situ TiB2+Mg2Si/Al-2Mg matrix composite are respectively improved by 21.55% and 15.44% in comparison with Mg2 Si aluminum-matrix composites, but its brittleness has not been completely changed.